# HACKING -*- org -*- #+TITLE: Hacking notes for Libgcrypt #+STARTUP: showall * How to contribute The following stuff explains some basic procedures you need to follow if you want to contribute code or documentation. ** No more ChangeLog files Do not modify any of the ChangeLog files in Libgcrypt. Starting on December 1st, 2011 we put change information only in the GIT commit log, and generate a top-level ChangeLog file from logs at "make dist" time. As such, there are strict requirements on the form of the commit log messages. The old ChangeLog files have all be renamed to ChangeLog-2011 ** Commit log requirements Your commit log should always start with a one-line summary, the second line should be blank, and the remaining lines are usually ChangeLog-style entries for all affected files. However, it's fine -- even recommended -- to write a few lines of prose describing the change, when the summary and ChangeLog entries don't give enough of the big picture. Omit the leading TABs that you're used to seeing in a "real" ChangeLog file, but keep the maximum line length at 72 or smaller, so that the generated ChangeLog lines, each with its leading TAB, will not exceed 80 columns. ** License policy Libgcrypt is currently licensed under the LGPLv2+ with tools and the manual being under the GPLv2+. We may eventually update to a newer version of the licenses or a combination of them. It is thus important, that all contributed code allows for an update of the license; for example we can't accept code under the LGPLv2(only). Libgcrypt used to have a strict policy of requiring copyright assignments to the FSF. To avoid this major organizational overhead and to allow inclusion of code, not copyrighted by the FSF, this policy has been relaxed. It is now also possible to contribute code by asserting that the contribution is in accordance to the "Libgcrypt Developer's Certificate of Origin" as found in the file "DCO". (Except for a slight wording change, this DCO is identical to the one used by the Linux kernel.) If your want to contribute code or documentation to Libgcrypt and you didn't signed a copyright assignment with the FSF in the past, you need to take these simple steps: - Decide which mail address you want to use. Please have your real name in the address and not a pseudonym. Anonymous contributions can only be done if you find a proxy who certifies for you. - If your employer or school might claim ownership of code written by you; you need to talk to them to make sure that you have the right to contribute under the DCO. - Send an OpenPGP signed mail to the gcrypt-devel@gnupg.org mailing list from your mail address. Include a copy of the DCO as found in the official master branch. Insert your name and email address into the DCO in the same way you want to use it later. Example: Signed-off-by: Joe R. Hacker (If you really need it, you may perform simple transformations of the mail address: Replacing "@" by " at " or "." by " dot ".) - That's it. From now on you only need to add a "Signed-off-by:" line with your name and mail address to the commit message. It is recommended to send the patches using a PGP/MIME signed mail. ** Coding standards Please follow the GNU coding standards. If you are in doubt consult the existing code as an example. Do no re-indent code without a need. If you really need to do it, use a separate commit for such a change. * Porting hints ** Taking optimized MPI code out of GMP: I generated the pentium4/* files by glueing the existing assembler prologues to the GMP 4.2.1 assembler files generated with the m4 tool in GMP's build process, for example: $ m4 -DHAVE_CONFIG_H -D__GMP_WITHIN_GMP -DOPERATION_rshift -DPIC \ rshift.asm >tmp-rshift.s Then tmp-rshift will contain the assembler instructions for the configured platform. Unfortunately, this way the comments are lost. For most files I re-inserted some of the comments, but this is tedious work. * Debug hints ** Debugging math stuff: While debugging the ECC code in libgcrypt, I was in need for some computer algebra system which would allow me to verify the numbers in the debugging easily. I found that PARI (pari-gp package in Debian) has support for elliptic curves. The below commands shows how they are set up and used with an example. ===8<======== hextodec(s)=local(v=Vec(s),a=10,b=11,c=12,d=13,e=14,f=15,A=10,B=11,C=12,D=13,E=14,F=15,h);if(#setunion(Set(v),Vec("0123456789ABCDEFabcdef"))>22,error);for(i=1,#v,h=shift(h,4)+eval(v[i]));h p = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF") a = hextodec("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFC") b = hextodec("51953EB9618E1C9A1F929A21A0B68540EEA2DA725B99B315F3B8B489918EF109E156193951EC7E937B1652C0BD3BB1BF073573DF883D2C34F1EF451FD46B503F00") /* Set up y^2 = x^3 + ax + b mod (p). */ e = ellinit(Mod(1,p)*[0,0,0,a,b]); gx = hextodec ("00C6858E06B70404E9CD9E3ECB662395B4429C648139053FB521F828AF606B4D3DBAA14B5E77EFE75928FE1DC127A2FFA8DE3348B3C1856A429BF97E7E31C2E5BD66") gy = hextodec ("011839296A789A3BC0045C8A5FB42C7D1BD998F54449579B446817AFBD17273E662C97EE72995EF42640C550B9013FAD0761353C7086A272C24088BE94769FD16650") g = Mod(1,p)*[gx,gy] n = hextodec ("01FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFA51868783BF2F966B7FCC0148F709A5D03BB5C9B8899C47AEBB6FB71E91386409") /* Verify that G is on the curve, and that n is the order. */ ellisoncurve (e,g) isprime (n) ellpow (e,g,n) d = hextodec ("018F9573F25059571BDF614529953DE2540497CEDABD04F3AF78813BED7BB163A2FD919EECF822848FCA39EF55E500F8CE861C7D53D371857F7774B79428E887F81B") qx = hextodec ("00316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B3B") /* Note: WRONG! (It is apparent that this is the same as X shifted by 8 bit). */ qy = hextodec ("0000316AAAD3E905875938F588BD9E8A4785EF9BDB76D62A83A5340F82CB8E800B25619F5C3EA02B7A4FA43D7497C7702F7DFBEAC8E8F92C3CAABD9F84182FDA391B") q = Mod(1,p)*[qx,qy] /* Calculate what Q should be given d. */ ellpow (e,g,d) /* This is not 0 and thus shows that libgcrypt gave Q and d that do not match. */ ellpow (e,g,d) - q ====8<=====================